The invention is generally directed to a reflow soldering apparatus and method. More particularly, a reflow soldering apparatus and method are provided for selective infrared radiant heating alone or in combination with convection heating for solder mounting electrical and electronic components to surfaces of circuit boards.
Reflow soldering systems provide high volume soldering of surface mount electronic components to circuit boards and other electronic substrates using radiant and convection heating. Many reflow soldering techniques have a tendency to overheat components, causing thermal damage to heat-sensitive and small components. Use of convection heating in conjunction with radiant heating helps to reduce the risk of overheating components due to the thermal leveling effect provided, in part, by convection heating. The combination of convection and radiant heating, however, does not address the problem of uniformly heating components of different sizes on a single circuit board. As the size differential between individual components and circuit boards increases, heating components to a substantially uniform temperature becomes more difficult. Flip chip designs, such as cell phone and optical communications chips, have higher heat outputs on the order of approximately 80 watts/cm2 in comparison to other components, such as integrated circuits, having heat outputs of approximately 2 watts/cm2. These flip chip designs often require the attachment of heat sinks in order to dissipate the substantial heat output, which increases the overall size of the flip chip components. Reflow soldering systems and techniques that use a combination of convection heating and radiant heating, provided as infrared (IR) heat, are susceptible to overheating or under heating large components.
In addition, use of lead-free solders in surface mount applications requires precision in controlling the temperatures of components and circuit boards to the desired ranges of temperatures in the various phases of reflow soldering. In particular, lead-free solders often require high melting temperatures and narrow process windows between the peak temperatures required just below the desired reflow temperature and the liquidous temperatures required to reflow solder. Lead-free soldering, thus, requires accurate temperature control and heating of components and circuit boards.
Therefore, it is desirable to provide an improved reflow soldering apparatus and method using a combination of infrared radiant heating and convection heating, whereby control of narrow ranges of temperatures is achieved and surface mount components of different sizes are substantially uniformly heated to within desired ranges of temperatures during the reflow soldering process. It is desirable to provide a reflow soldering apparatus and method with efficient overall performance providing energy savings and high process throughput.
An object of the invention is to provide an improved reflow soldering apparatus and method. Another object of the invention is to provide an infrared heating assembly for selective infrared heating.
In general, in an aspect, the invention provides a reflow soldering apparatus for soldering one or more components to a circuit board comprising a housing having a conveyor to convey the circuit board through the housing, at least one heating zone disposed in the housing, and at least one infrared heater disposed in the heating zone. The at least one infrared heater is spaced from the conveyor to heat one or more of the components disposed on the circuit board as the circuit board is conveyed through the heating zone, and is disposed and configured to selectively heat one or more of the components as they are conveyed through a line-of-sight of the at least one infrared heater.
Implementations of the invention may include one or more of the following features. The apparatus can further comprise at least a second infrared heater, the second infrared heater being spaced from the conveyor to heat one or more of the components disposed on the circuit board as the circuit board is conveyed through the heating zone, and being disposed and configured to selectively heat one or more of the components as they are conveyed through a line-of-sight of the at least one infrared heater. The at least one infrared heater is located above the conveyor, or, alternatively, the at least one infrared heater is located below the conveyor. The apparatus can further comprise at least one side infrared heater spaced being spaced from the conveyor to heat one or more of the components disposed on the circuit board as the circuit board is conveyed through the heating zone, the at least one infrared heater being disposed and configured to selectively heat one or more of the components as they are conveyed through a line-of-sight of the at least one infrared heater.
Implementations of the invention may further include one or more of the following features. The apparatus can comprise a control system operatively coupled to the apparatus to control operation of the at least one infrared heater. The control system can include a programmable controller to control operation of the at least one infrared heater. The programmable controller can include at least one stored variable. The apparatus can further comprise at least one sensor disposed in the heating zone, the at least one sensor being configured to detect at least one variable of operation of the heating zone such that when the sensor detects the at least one variable, the sensor sends a signal to the programmable controller, and the programmable controller, in response to receipt of the signal, controls the operation of the at least one infrared heater. The programmable controller can selectively control the operation of the at least one infrared heater. The apparatus can further include a temperature sensor that detects a temperature in the heating zone such that the sensor sends a signal to the programmable controller corresponding to the temperature and the programmable controller, in response to receipt of the signal, controls the operation of the at least one infrared heater. The programmable controller can compare the signal sent by the temperature sensor to at least one stored variable to selectively operate the at least one infrared heater. The apparatus can include an optical sensor that detects the circuit board in the heating zone such that the sensor sends a signal to the programmable controller corresponding to detection of the circuit board and the programmable controller, in response to receipt of the signal, controls the operation of the at least one infrared heater. The programmable controller can compare the signal sent by the optical sensor to at least one stored variable to selectively operate the at least one infrared heater.
The apparatus can include at least one infrared heater disposed in an array of infrared heaters. The apparatus can further include the at least one infrared heater disposed in a linear array of infrared heaters, the linear array being disposed and configured to extend above and across the conveyor in a substantially perpendicular orientation to a direction in which the conveyor conveys the circuit board.
These and other advantages of the invention, along with the invention itself, will be more fully understood after a review of the following figures, detailed description, and claims.